Ship&#39;s maneuver assessment system

ABSTRACT

A ship&#39;&#39;s maneuver assessment system is provided as a radar system accessory for permitting identification of intruding ships that demonstrate collision threat characteristics and for the generation of a maneuver assessment display providing the ship&#39;&#39;s operator with an evaluation of possible maneuvers for avoiding collision with such intruding vessels.

United States Patent [191 Riggs 111 3,717,873 Feb. 20, 1973 [54] SHIP'SMANEUVER ASSESSMENT SYSTEM [75] Inventor: Robert F. Riggs,Charlottesville, Va.

[73] Assignee: Sperry Rand Corporation 22 Filed: Nov. 5, 1970 21 Appl.No.: 87,025

[52] US. Cl. ..343/5 EM, 343/112 CA [51] Int. Cl ..G01s 7/22 [5 8] Fieldof Search ..343/5 EM, 112 CA [56] References Cited UNITED STATES PATENTS3,188,631 6/1965 Birtley ..343/5 EM 2,603,775 7/1952 Chipp ..343l5 EM3,307,177 2/1967 Novak ..343/5 EM 3,355,733 11/1967 Mitchell et al..343/5 EM Primary Examiner-Benjamin A. Borchelt Assistant ExaminerG. E.Montone Attorney-S. C. Yeaton [5 7] ABSTRACT A ships maneuver assessmentsystem is provided as a radar system accessory for permittingidentification of intruding ships that demonstrate collision threatcharacteristics and for the generation of a maneuver assessment displayproviding the ships operator with an evaluation of possible maneuversfor avoiding collision with such intruding vessels.

8 Claims, 4 Drawing Figures PAm-marzszow Y 3,717,873-

manor} 0x GYROOOMPASIS ZZ RADAR T. w.s. SYSTEM SYSTEM 24 T32/l 1j ItCOMPUTER 1 TIMER IN'VE/VTOI? "AI E/v5) ROBERT Fl-fi/aas PATfimmrsazoma3,717,873 sum 20F 2' CONE OF .OWN HISTORY INTERCEPT POINT (POSSIBLECOLLISION) TARGET HISTORY LINE PROJECTION ON X-Y PLANE X owm HEADINGPROJECTION ON x-Y PLANE PRESENT POSITION possuaus COLLISION ROBERT F.f-P/aas AT TUR/Vt Y;

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SHIP'S MANEUVER ASSESSMENT SYSTEM BACKGROUND OF THE INVENTION 1. Fieldof the Invention The invention pertains to radio means for early warningand assessment of potential collision between moving vehicles and moreparticularly relates to means adaptable for use with azimuth scanningradar systems or the like for generating cooperating displays, oneproviding a readily interpretable presentation of factors indicatingcollision possibilities and a second providing a quickly and accuratelyinterpretable display for assessing consequent ship maneuvers designedsafely to eliminate the collision possibility.

2. Description of the Prior Art Radio and other aids to marinenavigation have been employed in the past for augmenting the lookoutsability visually to determine potential collisions between marinevessels. Radar systems and similar sensors have been used to determinethe bearing rate and range data corresponding to a selected intrudervessel. However, the detection of small bearing rates at large rangesdoes not lend itself to accurate instrumentation, since small errorsbetween successive bearing readings destroy the accuracy of predictionof the closest point of approach of the intruding vessel.

Collision warning techniques often employ measurement of passingdistance at closest point of approach. In such a system, radarindicators, reflection plotters, and plotting tables are often used.However, errors of plotting can seriously degradate the reliability ofthese methods. Generally, a single operator cannot accurately plot thedata and assess from it the degree of danger attached to as few as threeintruding targets simultaneously. Semi-automatic transfer of radar toplotting boards has been attempted, but the instrumentation isexpensive. Also proposed have been quite expensive though more accuratephotographic plotting systems; in these photographic systems, few errorscan be introduced by the operator.

Typical collision warning systems of the above described type do not ina fully accurate or rapid manner furnish data directly usable inreliably assessing what maneuver own ship must make in order effectivelyto avoid an impending collision. The ship's operator must, uponobservation of a collision potential, apply various rules and customssuch as the International Rules of the Road and the Inland Rules of theRoad which have been devised to prevent collisions. The Steering andSailing Rules must also be followed when there is risk of collision. Itis left to the ships operator after the warning of an impendingcollision to exercise a difficult judgment as to what maneuver he mustorder the ship to make so as to remove the risk of collision. Therequired space for a safe maneuver depends upon knowledge of manyfactors, such as knowledge of the intruding vessel's class, speed,intention, and heading. Adverse wind and sea states can be influentialin causing erroneous maneuvers leading to disaster rather than toevasion.

SUMMARY OF THE INVENTION The invention is a collision avoidance andmaneuver assessment aid for marine vessels of the type employing a radarplan position display generated by an azimuth scanning radar unit. Anovel system first warns of intruding vessels and determines which arethreats, such as by employing the tau collision avoidance criterion. Theparameters of closing-range targets, when such targets are identified asdangerous, are selectively transferred in order of hazard level totrack-while-scan apparatus for coordinate storage and coordinate rategeneration. The stored data, when extracted from the track-while-scanunit, is modified for inertial stabilization and other purposes and isemployed to generate a synthetic cathode ray display for maneuverassessment. The particular synthetic display and a novel symbolgraphically representing the target or hazard ships history permitaccurate and rapid judgment by an observer of permissible maneuvers bywhich the ship may avoid the collision possibility.

The maneuver assessment display indicates points of probable collision,rather than closest point of approach between own ship and an intrudingvessel, and displays a calculated area of uncertainty about each pointof probable collision. All points of probable collision are displayedsimultaneously for recognized intruders entered into the assessmentsystem, all intruding target's present positions and predicted tracks totheir associated points of probable collision also being presented.Thus, true headings for each such intruder are readily observed,permitting ready compliance with the established rules of the road. Thedisplay of area of uncertainty also permits the operator to choose asafe heading without trial headings or guess-work.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the screen ofa cathode ray tube showing symbols used in the display of the presentinvention.

FIGS. 2a and 2b are respectively threeand twodimensional graphicrepresentations useful in explaining the theory of operation of theinvention.

FIG. 3 is a block diagram illustrating one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The collision avoidance andcollision assessment apparatus of the present invention provides asynthetic display normally generated by a cathode ray tube indicator anddesigned to present to the viewer all information needed for performingan effective maneuver whenever risk of collision with an intruding shipis established. The display, as indicated in FIG. 1, is by way ofexample an offset type P display, representing the position of own shipat the location 1 near the bottom of the indicator screen 2. A headingflash cursor 3 is normally directed vertically or across screen 2 in thepresentation, being formed by a conventional heading flasher circuit soas to extend from location 1 substantially to the opposite side ofscreen 2. The heading cursor 3 thus represents the future track of ownship unless own ships course is to be disturbed.

Other indications formed of straight lines and circles appear on thescreen 2 of FIG. 1. Each represents characteristics of ships in thelocality of own ship; for example, the end 5 of line 4 represents thepresent position of a target ship which might be regarded as anintruder. The straight line 4 indicates the intruding targets futuretrack. As will be further described, the circle 6 formed about the end 7of future track 4 represents a locale of possible collision between thevessel now at position 5 and own ship. Each such region of possiblecollision represents an area of uncertainty as to the exact location ofthe end 7 of targets future track 4. It is seen that the intrudingvessels heading is represented by the direction of the targets futuretrack line 4. Relative speed between the intruder and own ship 1 isrepresented by the ratio of the length of the predicted track 4 to ownships range to the region of possible collision. In some circumstances,such as represented by circles 8 and 9 as when the hazard is overtakingown ship, there may be two regions of possible collision.

It is to be understood that other symbols may be added to the displayindicated in FIG. 1. For example, a transparent map display showingfixed hazards such as land masses may be superimposed over screen 2 andmay be automatically moved relative to screen 2 in time with own shipsapparent motion along the heading cursor 3, using data, for instance,from gyrocompass 40 and ships speed sensor 41 as shown in FIG. 3. Videosuperposition of such symbols as appear on a data chart may be added bya flying spot scanner, permitting the display and ready identificationof both fixed and moving hazards on a single display. Furthermore, if aminimum passing distance at the closest point of approach by the vessels1 and 5 is desired, for example, the circular symbol 6 may be enlargedso that its radius represents the sum of the selected minimum passingdistance value and the calculated uncertainty in the position ofpossible collision.

It will be clear to those skilled in the cathode ray display art thatany of several well known approaches may be used in tracing symbols onthe face 2 of the cathode ray tube. Type I scansion or raster scansionof the electron beam may be employed within the scope of the invention,each symbol being drawn by intensification of the electron beam as it isdeflected across the locus of the symbol. It is furthermore apparent toone skilled in the art that symbols may be drawn by well known meansduring the fly-back or re-trace time between each such electron beamdeflection, for example, by one or by a series of deflections of theintensified beam during the fly-back time in a raster scanning system.Such methods are well known in the art, as also are methods in which theregular polar or raster scanning of the intensified electron beam is notused. In such apparatus, symbols are generated by forming a programmedseries of deflection strokes to form a symbol.

The concepts and the principles to be employed in producing the displayof FIG. 1 may be visualized by inspection of the three dimensionalrepresentation shown in FIGS. and 2b. In FIG. 2a, an XY plane isprovided that represents the surface of the earth. Accordingly, movableships and fixed hazards such as land masses all occupy positions on theXY plane. The passage of time in the events involving own ship andintruding vessels is represented by the vertical axis T. This behavioras a function of time, which may be spoken of as the ships history, maybe represented by a straight line suitably oriented in the threedimensional space X-YT. Own ship's position is again represented atlocation 1 which is the origin of the X- Y-T coordinate pattern. Thelocation 1 corresponds in position and instantaneous time to thelocation 1 on the screen 2 of FIG. I.

It will be assumed, by way of example and without loss in generality,that own ship 1 is moving in the XT plane of FIG. 2a at some fixed speedV The angle that own ship's history line 10 makes with the time axis Tis then tan lV l. In the coordinate system of FIG. 2a, a collisionbetween own ship and an intruder ship will occur if own ships historyline, such as line 10, intercepts the history line of any other ship. Ifown ship elects to ake a course change maneuver such as an evasive rnneuver without changing speed, own ships history line will continue tolie on the cone of own ships history, which is defined by using line 10by revolving it about the time axis T so as to generate a cone having anapex angle 2 tanl V, At any location at which some other ships historyline intercepts the cone of own ships history, the intercept between theother ships history line and the cone of own ships history represents apoint of probable collision.

In implementing the solution of equations which follow from the geometryof FIGS. 2a and 2b, it will be understood that a variety of types ofknown sensor, computer, and symbol generator devices may be successivelyemployed. In particular, the computer so employed must solvesimultaneous equations representing the cone of own ships history andthe target history line or at least a history line representing the best1 available estimate of the targets history line. The angle of thehazards history line with respect to the vertical axis is tan IV l whereIV I is the best estimate of the targets speed. The projection of thethree dimensional figure shown in FIG. 2a on the planar representationof FIG. 2b is seen to be similar to the display for a representativehazard vessel as discussed in connection with FIG. 1. For example, theprojection of the target or hazard history line onto the XY planecorresponds in FIG. 2b to be the targets future track with the directionof that track representing the heading of the intruding vessel.

To illustrate the general problem of simultaneous solution to be solvedby the system computer, it is seen that the cone of own ships history ofFIG. 2a may be represented by:

x +y V32 1 Since the targets future track may justifiably be assumed tobe substantially its history line, that line representing the targetsfuture track may be designated in terms of X and Y coordinate positionsand coordinate rates by the set of equations:

r= m+ r (2) yr yor )"r where x y are present position coordinates of theintruder or hazard in the XY (earth) plane and .t, y are correspondingvelocity components. Simultaneous solution of equations (1), (2), and(3) yields the time to the point of probable collision (the end 7 ofvector 4 in FIG. 1):

The solution in equation (4) for the time tppc can be substituted intoequations (2) and (3) to obtain the actual x,y coordinates of any actualpoint of probable collision. Since the usual marine radar systemprovides target position data in polar p, 0 coordinates, a coordinatetransformation to x, y values will be required if the presentation onscreen 2 is to be provided by raster scanning the cathode ray beam or ifcomputation is performed in x,y coordinates.

If the radical in equation (4) becomes imaginary; i.e., if:

Mar 7dr? l or 'yofi then a collision is not possible. In such a case,the circle 6 or other figure representing uncertainty can be droppedfrom the display. The area of uncertainty can be enlarged to account fora desired minimum passing distance.

The size of the circular or other area of uncertainty surrounding thepoint 7 of probable collision can be calculated by a computer in severalways. By one method, the extreme values of x and y are calculateddirectly from equations (1), (2), and (3) by arbitrarily substitutingextreme values of the estimates of i}, y x y and V Another suitableapproach is to calculate the variance of the estimates of these samevariables, following the least squares fit routine and then tosubstitute these values of variances within equations (1), (2), and (3).The radius of the area of uncertainty can then be taken as equal to somelow'multiple such as two or three of the square root of the variance inx and From FIG. 2a, the distinction between the point of probablecollision and the closest point of approach between the two vessels isclear. The time to closest point of approach is determined when aminimumoccurs in the quantity:

where x is the position of own ship as a function of time along theX-axis, provided own-ship maintains present course and speed. Also, y isthe position of own ship as a function of time along the Y-axis,provided own ship maintains present course and'speed. It will be assumedthat the coordinate system remains fixed on the surface of the earth.

From the foregoing discussion, it is clear that a concept using thepoint of probable collision criterion is a much more useful concept thanis the prior art closest point of approach concept in avoiding collisionbetween vessels through adequately assessing a proposed collisionavoidance maneuver. In the system of the present invention, all pointsof probable collision are displayed simultaneously and can be visualizedas relatively fixed obstacles to be avoided in any selected maneuver.For example, when own ship changes heading, the time of closest point ofapproach changes radically and in a manner difficult to visualize.Knowing only the coordinates of the presently predicted closest point ofapproach does not permit the prediction of the heading or headings ofown ship which may result in a collision. Conversely, a

knowledge of the coordinates of a presently predicted closest point ofapproach does not clearly inform the ships pilot as to heading orheadings that must be avoided. The character of displays emphasizing theclosest point of approach criterion is indeed such that it is possibleto predict closest point of approach data corresponding to only onethreat at a time.

It is evident by inspection of the foregoing analysis that solution ofthe equations thereby generated may be accomplished by several knownmethods, including the use of a cooperative assembly of known analog orknown digital data processing or computing circuits. For example, theseveral equations involve simple arithmetic operations such as addition,subtraction, multiplication, squaring, and extraction of square roots.Many examples of both analog and digital computer elements are availablein the prior art for accomplishing such computations and it is wellknown that they may readily becoupled together in cooperative relationfor attaining desired results. It is furthermore evident that aconventional general purpose digital or analog computer may be employedfor the purpose. It is obviously well within the ordinary skill ofdigital computer programmers to process the equations discussed above,to create flow charts, and to translate the latter into computerroutines and sub-routines for solution of such equations along with acompatible computer language for processing input data and instructionsto produce outputs directly useful for application in a standard cathoderay tube display.

FIG. 3 represents one possible instrumentation for practising theinvention and incorporating the novel maneuver assessment display 20. Aspreviously indicated, the system uses data derived, for example, by aconventional azimuth scanning pulse radar system 21 of the type widelyused in marine radar applications and employing a directiveazimuth-scanning antenna 21a. In the invention, the radar antennaazimuth or hearing data and detected target range data may be used togenerate in a conventional way, a type P or plan position presentationon the screen of display 22. Thus, when the display is an off-set type Pdisplay, all targets in the vicinity of radar 21 are periodicallyintensified on the screen of display 22. Target 22a represents one suchtarget, while the location of own ship is represented at 1. Additionaltargets will generally appear on display 22, along with reflections fromfixed obstacles including land masses, if present. Variants of theregular type P display may be used, such as an offset type P display andothers. Further, certain characteristics of images such as that oftarget 22a may be modified to enhance rapid recognition of thoserepresenting dangerous targets, as is customarily done in collisionwarning displays using the tau criterion principles which providedisplays improving the operators ability to discriminate between realand potential threats and non-threats. However, the simple type Pdisplay is by inherent nature a collision warning display and so it isplaced in FIG. 3 as representative of collision warning or collisionassessment displays in general.

As noted, several targets will often appear on display 22, each having agreater or lesser hazard characteristic with respect to own ship 1. Theoperator of own ship 1 Entry of the coordinates of the selected targetis accomplished by placing a conventional light-sensitive pick up 23 orlight-pen or other transducer over the location of the selected targetimage. Such a pick up device is illustrated in use in the Frank Pat. No.3,182,320, issued May 4, 1965, and covering an Automatic Range andAzimuth Track While Scan System. At the time that the target image isnext intensified, an electrical pulse is transmitted via lead 24 totrackwhile-scan system 25, which system also receives synchronizing andother signals via lead 26 from radar unit 21.

Track-while-scan system 25, like radar unit 21, is not necessarily anovel part of the system, as suitable devices for practising itsfunction are present in the prior art. Track-while-scan systems are ofthe general class of devices known as devices for tracking grouped orperiodically interrupted data and their theoretical basis is explainedby W. B. Jones and R. I. Hulsizer in Section 9.8 (page 378 et seq.) ofVolume 20 of the Radiation Laboratory Series: Electronic TimeMeasurements. Practical forms of these devices, which may be analog ordigital in instrumentation, are described in several U.S. patents suchas, for example, in the White U.S. Pat. No. 2,849,707 for a PositionCorrecting Means for Track-While-Scan Channels, issued Aug. 26, 1958; inthe Coveley U.S. Pat. No. 2,944,253 for a Radar System and Display,issued July 5, 1960; in the Close U.S. Pat. No. 3,064,250 for anAutomatic Track-While Scan Channel, issued Nov. 13, 1962, and elsewhere.

According to prior practice, such devices as optical pick up 23 havebeen used to enter coordinate data characterizing a selected targetappearing on a type P or other cathode ray indicator 22 into storage ina track-while-scan device, such as apparatus 25, where its rectangularor polar coordinates may be stored. Automatic lock-on in theconventional manner by apparatus 25 to signals received directly viaconductor 26 from the receiver of radar 21 at the time the antenna 21anext sweeps past the selected target automatically corrects the storedpositional data of the selected target after its initial entry until theoperation is manually disabled. Thus, for example, coordinates x and yand rates and y may be stored for any such target. Entry of a new ornext apparently dangerous target generates a second set of x,y,ir, and ydata for storage within trackwhile-scan apparatus 25 for the newlyselected target. Such stored x,y,.ic, and data may be stored at the willof the operator in this manner for a plurality of intruding vessels forsupply, upon demand, as on a time shared basis, via conductors 27 tocomputer 28. As previously noted, track-while-scan apparatus 25 may beeither of analog or digital nature and may be supplied, if required, ina conventional manner by suitable analog-to-digital or digital-to-analogconverters as interface elements between various components of thesystem such as apparatus 25 and computer 28. It will be understood thattrack-while-scan apparatus 25 is actually a type of computer device initself, performing arithmetic functions such as differentiation, andstoring data. It will therefore be understood that its function may beperformed either in a discrete unit, such as in the separate apparatus25, or that its arithmetic and storage operations may be performed byrespective arithmetic and storage elements present in computer 28. Thelatter elements may perform other system functions in a conventionalmanner on a time sharing basis.

Referring again to FIG. 1, it will be seen that computer 28 has severalcomputations to perform in generating the maneuver assessment symbols onthe indicator 20 of FIG. 3. It will be demonstrated how the system isconstructed and how it operates to generate one such symbol such as thesymbol including symbol elements 4, 5, 6, and 7 shown in FIG. 1. It willbe appreciated that the stored at and y coordinates of the varioustargets are readily available in the track-whilescan unit 25. Since themotions of each of the ships in the vicinity of own ship are relativelyslow compared to the speeds of even the simplest computers, it is seenthat it is not necessary to compute all of the data in real time and,consequently, the threat or hazard data is conveniently stored andup-dated only periodically by track-while-scan system 25. Thus, therewill be little difference between the actual x and y coordinates of aparticular target and the corresponding stored x and y coordinatesderived by computer 28 from track-whilescan system 25. It will also beunderstood that a plurality of symbols such as that made up of elements4,5,6, and 7 of FIG. 1 may readily be generated on a time sharing ormultiplexing basis using simple time sharing techniques well known inthe analog and digital computer arts.

Referring now particularly to the apparatus for generating a compositesymbol made up of elements 4,5,6, and 7, it is apparent that the x and ycoordinates of the point 5 in FIG. 1 substantially represent the presentrectangular coordinates of a target or hazard vessel. In the following,it will be understood that the discussion of the location 5 and of thecoordinate characteristics of other elements of the symbol could equallywell be discussed in the same manner if polar p, 0 coordinates were inactual use in the system under discussion. Computer 28 may be suppliedwith a selfcontained clock or timing system which dominates theoperation of other elements of the system, or it may be under thecontrol of a separate timer 29. For example, timer 29 may besynchronized using lead 30 to a clock internal of computer 28. On theother hand, timer 29 may represent the major system clock, determiningthe timing of computer 28 by the agency of signals transmitted to it viaelectrical lead 30. In what follows, the timer 29 will, as a matter ofconvenience, be spoken of as the basic timer or clock control for thesystem.

It is apparent that computer 28 may be programmed so as periodically toderive, from track-while-scan system 25, the x and y coordinates oflocation 5 shown in FIG. 1, and to supply by well known means coordinatevalues as control signals to display 20 and thus to cause the cathoderay beam to be instantaneously intensified so as to form a bright spotat point 5 on display 20.

The next function of the computer 28 is to cooperate with the linesymbol generator 31 in forming the predicted track 4 of FIG. 1. As isseen from the foregoing theoretical analysis, the track 4 is drawn fromtarget present position to a predicted point 7 of probable collisiondetermined by the relative bearing of the target vessel and its speed.Computer 28 applies via lead 32 x and y coordinates of point 5 to theline symbol generator 31, and also supplies via leads 33 x and ycoordinates of the predicted point 7, having used the x,y,:'c, and yinformation generated by track-while-scan system 25 to generate suchvalues. Line symbol generator 31 may then supply, substantiallyinstantaneously following the intensification of point 5, componentsweep voltages via leads 34 and 34a for generating line 4. Apparatussuitable for performing the function of line symbol generator 31, bothin analog and digital forms, is well known in the art. Both in thepatent and other literature, there appears a substantial number ofdisclosures showing means for the generation, for instance, on a cathoderay tube screen, of a line of adjustable length, starting at anyselected coordinate location on the cathode ray tube screen and endingat any other coordinate location on the cathode ray screen, andtherefore lying at any arbitrary angle with respect to the operatingcoordinate system.

A simple arrangement which may be adapted to forming the target futuretrack line 4 appears, for example, in the J. E. Shepherd et al. U.S.Pat. No. 2,406,858 for a Visual Position and Phase Sense Indicator,issued Sept. 3, 1946 and assigned to the Sperry Rand Corporation. Theart of drawing vectorial lines is a highly exploited cathode ray tubeart in the field of character displays. For example, many such characterdisplay circuits employ symbol generators in which the sweeping of thecathode ray beam in a repetitive organized pattern is not employed. Onthe other hand, the method employed in such alphanumeric symbolgenerators is that of assembling the symbol by a concatenation ofsuccessive electron beam traces. Each succeeding trace generally beginsat the point defined by the end of the immediately preceding trace. Itwill be apparent that in drawing usual alphanumeric symbols, thesuccessive traces are generally vectored at changing angles. It isapparent that each such elemental trace is generated by apparatus whichstarts the trace at an arbitrary location on the cathode ray tube andends the trace at another arbitrary location. Examples of such systemsare found in the Bacon U.S. Pat. No. 3,325,802 for a Complex PatternGeneration Apparatus, issued June 13, 1967; in the Dye U.S. Pat. No.3,394,367 for a Symbol Generator, issued July 23, 1968; in the TownsendU.S. Pat. No. 3,289,195, for a Delay Line Wave Shape Generator, issuedNov. 29, 1966, and elsewhere.

Accordingly, the vector 4, representing the predicted trajectory of thetarget vessel has been drawn between the points 5 and 7, which point 7has been defined in the foregoing as the point of probable collision.The x and y coordinates of location 7 remain available in a computer 28and are now used in generating a boundary 6 of a region representing aregion of possible collision surrounding the point of probable collision7. At the instant at which the trajectory line 4 is being drawn, thecoordinates of point 7 are made available within computer 28.Accordingly, if the region of possible collision 6 is to be indicated asbounded by a circle surrounding point 7, computer 28 establishes thesize of that uncertainty region by computing, for example, a radius forcircle 6. Computer 28 then supplies x and y coordinates of point 7 tothe circle symbol generator 35 via leads 36 and 37. The deflectionvoltages for a circle of appropriate size are supplied via leads 38 and38a in a conventional manner in indicator 20 to produce the circle 6.The size of circle 6 may be increased by an incremental safety factor bymanipulation of control 35a.

Circle symbol generators suitable for application in apparatus 35 arewell known in the art. In fact, this particular alphanumeric symbol isthe easiest and most commonly generated symbol in prior art charactergeneration equipment. Apparatus for drawing a circle about any desiredpoint on a cathode ray tube screen is thus well known. For example, anequipment adaptable for this purpose is illustrated in the Courter U.S.Pat. No. 3,283,317 for Symbol Generators, issued Nov. 1, 1966 andassigned to the Sperry Rand Corporation. The Courter patent makes itclear how characters and symbols can be generated using cooperatingcircuits for generating whole or partial circles by the use of sinewaves and rectified components thereof. Other arrangements suitable forapplication in the present invention include those of the Uphoff U.S.Pat. No. 3,164,822 for a Diode Wave Form Generator for Symbol GenerationDuring the Retrace Interval of a Cathode Ray Tube, issued Jan. 5, 1965,and U.S. Pat. No. 3,164,823 for a Symbol Generating System for CRTDisplays Employing Retrace Insertion, issued Jan. 5, 1965, both beingassigned to the United States Government. Other patents illustratearrangements for generating circular symbols that may readily be appliedin the present system.

It is apparent that the line trace 4 and the circular symbol 6 may bedrawn simultaneously or nearly so, as desired. A dual gun cathode raytube employing corresponding sets of electrostatic deflection electrodesfor each electron beam permits drawing the line with one gun-beamdeflection system and the circle with the second gun-beam deflectionsystem. Single gun operation with a single deflection system may beused, for example, with the line being traced instantaneously prior tothe tracing of the circle.

The display 20 may employ an ordinary type of cathode ray tube in whichthe decay period of the phosphor on the display screen is selected sothat a symbol traced in the past has substantially faded by the timethat computer 28 calls for upgradingof the display. Regular or randomerasure of the display may also be accomplished under control ofcomputer 28 when a conventional direct viewing storage type of cathoderay display is employed. Such erasure may also be accomplished as in thepast at any time desired by the observer.

Variations of the system illustrated in FIG. 3 are readily apparent thatmay lend even greater versatility to the maneuver assessment displaysystem. It is seen that the optical pick off 23, or a similar device,may be used to pick off coordinate data from the display of a long rangeor early warning radar system or from a sonar display or other proximitywarning display or device. By means of the track-while-scan system 25,the operator may cause the system to lock on to and to track anyselected hazard detected by any available sensor. The relative bearingsand ranges of the targets locked into the automatic tracking operationare readily available in upgraded form for manipulation by computer 28for generating data required of symbol generators 31 and 35 forproducing display 20.

The data, while present in the computer 28, may be manipulated orrefined by the use of inertial stabilizing information such as generatedby gyrocompass 40 or ships speed sensor 41. In this manner, the threatbearing may be corrected for own ships roll, pitch, or yaw motions in aconventional manner as a refinement of the invention. Alternatively, thedata generated by the radar system may be provided with inherentstabilization features by the direct servo stabilization of antennascanner 21a. Functions not directly related to the collision avoidanceand maneuver assessment functions may also be performed by computer 28on a time sharing basis, such as inertial navigational functions and thelike.

While the invention has been described in its preferred embodiment, itis to be understood that the words that have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1 claim 1. Apparatus for providing a maneuver assessment display formobile vehicles comprising:

sensor means for generating coordinate and velocity component data of afirst vehicle with respect to a second vehicle, computing meansresponsive to said coordinate and velocity component data for computinga predicted track for said first vehicle to a point of probablecollision with said second vehicle and a region about said point ofprobable collision representing a region of possible collision, and

display means for displaying said predicted track and said regionrelative to each other.

2. Apparatus as described in claim 1 wherein said sensor meanscomprises:

azimuth scanning radar means for detecting coordinate data of said firstvehicle with respect to said second vehicle,

intermediate display means for displaying an image representing saidfirst vehicle,

transducer means for generating an electrical impulse uponintensification of said image on said intermediate display, and

means responsive to said impulse for automatically tracking and storingcoordinate and velocity component data characterizing said firstvehicle.

3. Apparatus as described in claim 1 wherein said computing meanscomprises digital computer means programmed to compute the terminalpoints of a said predicted track of said first vehicle.

4. Apparatus as described in claim 3 wherein said digital computer meansis programmed to calculate a dimension defining a region surroundingsaid point of probable collision representative of a region of possiblecollision.

5. Apparatus as described in claim 4 wherein said means for displaycomprises:

line symbol generator means under control of said digital computer meansand having first output means,

circle symbol generator means under control of said digital computermeans and having second output means,

cathode ray tube indicator means,

timing means for controlling said line symbol generator and said circlesymbol generator, and

means coupling said first and said second output means to said cathoderay tube indicator means for displaying said predicted track and saidregion.

6. Apparatus for providing a maneuver assessment display for mobilevehicles comprising:

sensor means for periodically detecting sets of coordinate data of afirst vehicle with respect to a second vehicle,

means for storing at selected times sets of said coordinate data,

means for calculating velocity components of said first vehicle fromsaid stored sets of coordinate data and for storing same, output meansadapted to supply the most recently stored of said sets of coordinatedata and the most recently computed of said velocity component data, I

means coupled to said output means for computing a predicted track forsaid first vehicle to a point of probable collision with said secondvehicle and a region about said point of probable collision representinga region of possible collision, and

means for displaying said predicted track and said region with respectto each other.

7. A display system for providing a maneuver assessment display forrepresenting first and second mobile vehicles characterized byparameters:

x y representing a first set of position coordinates of said firstvehicle,

x y representing a second set of position coor dinates of said firstvehicle at the time t of probable collision between said first andsecond vehicles,

1%,, 9, representing velocity components of said first vehicle at time rand V representing the speed of said second vehicle,

comprising: computer means responsive'to the application of measuredvalues of said parameters x y i y and V for solving a value of the saidparameter t using the equation:

two: OT :I yOTZJT "r 'l'y'r 0 OT T'lyOTgT) T -l-ZIT Q (ym +:voT

1 ZJT 0 and then by solving equation:

and equation:

by substituting said value of parameter tppc therein,

and

display means coupled to said computer means for automaticallydisplaying a line between locations on said display corresponding to theparameters x y and x y where the location 1: y defines the location ofprobable collision between said first and second vehicles.

8. Apparatus as described in claim 7 wherein:

said computer means responsive to the values of said parameters computesthe uncertainty of the location of the point of probable collisionbetween said first and second vehicles, and

said display means utilizes said uncertainty data to draw a boundarysurrounding location x y defining a region of possible collision betweensaid first and second vehicles.

* an a a: a

1. Apparatus for providing a maneuver assessment display for mobile vehicles comprising: sensor means for generating coordinate and velocity component data of a first vehicle with respect to a second vehicle, computing means responsive to said coordinate and velocity component data for computing a predicted track for said first vehicle to a point of probable collision with said second vehicle and a region about said point of probable collision representing a region of possible collision, and display means for displaying said predicted track and said region relative to each other.
 1. Apparatus for providing a maneuver assessment display for mobile vehicles comprising: sensor means for generating coordinate and velocity component data of a first vehicle with respect to a second vehicle, computing means responsive to said coordinate and velocity component data for computing a predicted track for said first vehicle to a point of probable collision with said second vehicle and a region about said point of probable collision representing a region of possible collision, and display means for displaying said predicted track and said region relative to each other.
 2. Apparatus as described in claim 1 wherein said sensor means comprises: azimuth scanning radar means for detecting coordinate data of said first vehicle with respect to said second vehicle, intermediate display means for displaying an image representing said first vehicle, transducer means for generating an electrical impulse upon intensification of said image on said intermediate display, and means responsive to said impulse for automatically tracking and storing coordinate and velocity component data characterizing said first vehicle.
 3. Apparatus as described in claim 1 wherein said computing means comprises digital computer means programmed to compute the terminal points of a said predicted track of said first vehicle.
 4. Apparatus as described in claim 3 wherein said digital computer means is programmed to calculate a dimension defining a region surrounding said point of probable collision representative of a region of possible collision.
 5. Apparatus as described in claim 4 wherein said means for display comprises: line symbol generator means under control of said digital computer means and having first output means, circle symbol generator means under control of said digital computer means and having second output means, cathode ray tube indicator means, timing means for controlling said line symbol generator and said circle symbol generator, and means coupling said first and said second output means to said cathode ray tube indicator means for displaying said predicted track and said region.
 6. Apparatus for providing a maneuver assessment display for mobile vehicles comprising: sensor means for periodically detecting sets of coordinate data of a first vehicle with respect to a second vehicle, means for storing at selected times sets of said coordinate data, means for calculating velocity components of said first vehicle from said stored sets of coordinate data and for storing same, output means adapted to supply the most recently stored of said sets of coordinate data and the most recently computed of said velocity component data, means coupled to said output means for computing a predicted track for said first vehicle to a point of probable collision with said second vehicle and a region about said point of probable collision representing a region of possible collision, and means for displaying said predicted track and said region with respect to each other.
 7. A display system for providing a maneuver assessment display for representing first and second mobile vehicles characterized by parameters: xOT, yOT representing a first set of position coordinates of said first vehicle, xT, yT representing a second set of position coordinates of said first vehicle at the time tPPC of probable collision between said first and second vehicles, xT, yT representing velocity components of said first vehicle at time tPPC, and VO representing the speed of said second vehicle, comprising: computer means responsive to the application of measured values of said parameters xOT, yOT, xT, yT, and VO for solving a value of the said parameter tPPC using the equation: 